1. Field of the Invention
The invention disclosed in this specification relates to a semiconductor device and a manufacturing method thereof.
2. Description of the Related Art
Attention has been focused on a technique for forming a transistor using a semiconductor thin film formed over a substrate having an insulating surface. The transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) or an image display device. Further, a technique using a wide band gap semiconductor such as an oxide semiconductor for a semiconductor thin film applicable to a transistor has been attracting attention.
For example, Patent Document 1 shows that an oxide semiconductor including an In—Ga—Zn—O-based oxide can be used for a channel formation region of a thin film transistor.